As with many inputs that may be used either in conventional or alternative farming practices, there is a need to examine the extent to which a product of interest may be effective in a particular situation. Results obtained from all farming inputs can differ greatly depending upon soil and climatic constraints at a given site, and this is no different for biological inputs. Indeed, results may be different in different areas of the same property, or even different areas of the same paddock, with variability between seasons also likely.

The first aspect to consider when deciding which products to trial is to understand what factors constrain production in the area in which the product will be trialled, and whether these are similar across the property. Some climate constraints such as drought susceptibility may be relatively widespread, whereas others such as waterlogging and frost may be very localised. Likewise, soil constraints can vary from local constraints such as shallow soil in some areas of a property, to more widespread issues such as excess acidity or alkalinity.

Seasonality and timing in relation to crop rotation may also affect results observed. For example, in an unexpectedly good rainfall year, a product that claims to help improve drought tolerance may have no observed effect, even though in a dry year it might have been effective. It is also known that soils can respond differently at different stages in a rotation e.g. after a legume or a break crop. Consequently, it is important to understand that, while the result observed in one year may either indicate that the product is effective (or not effective), it is quite likely that under different circumstances a different result may be observed.

Finally, even if rotations and climate were to remain constant, many products may have different results in the years after first application, even if the product is not reapplied. Long-lived products such as biochars may have long-term effects on soil physico-chemical properties because slow interactions occur between the biochar and the mineral soil. Other products aimed at manipulating the soil biological community may require several years of re-application before significant results are observed. Thus nature of the biological product being applied is of considerable importance.

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